The present invention relates to shaped articles of porous carbon comprising carbon fibers and a process for manufacturing the same. More in detail, the present invention relates to shaped articles of porous carbon of a large porosity, of a sharp distribution of pore radius thereof and of an excellent mechanical strength, and a process for manufacturing the same.
The shaped articles of porous carbon comprising carbon fibers have come to be regarded recently as more and more important in the fields of filter materials, base plates for electrodes in fuel cells and the likes. Particularly in the field of electrode substrate in fuel cells, shaped articles of porous carbon excellent in electroconductivity, chemical stability and mechanical strength with a large porosity and a sharp distribution of pore diameters thereof are required.
The shaped articles of porous carbon comprising carbon fibers are manufactured by the following various processes. As one of the processes, U.S. Pat. No. 3,829,327 discloses a process in which the web of carbon fibers is covered by chemical vapor deposition with carbon produced by thermal cracking of hydrocarbon. The paper of carbon fibers manufactured by the process of U.S. Pat. No. 3,829,327 is excellent in chemical stability, gas-permeability and electroconductivity, however, it is not economical in order to include the expensive step of chemical vapor deposition, and it has a demerit that the larger the porosity, the smaller the mechanical strength thereof. Another process for manufacturing sheet-likely shaped articles of porous carbon comprises adding an alcohol of boiling point of higher than 150.degree. C. as a binder to pitch fibers for manufacturing mats of pitch fibers and treating the mat of pitch fibers for carbonization in a non-oxidative atmosphere (refer to U.S. Pat. No. 3,960,601). According to the process of U.S. Pat. No. 3,960,601, although sheet-likely shaped articles of porous carbon excellent in electroconductivity with a large porosity are available, their mechanical strength is not necessarily excellent.
As a still another process, U.S. Pat. No. 3,960,601 also discloses the web of carbon fiber obtainable by infusibilizing and then carbonizing the webs comprising pitch fibers prepared by blow-spinning of a pitch. Although sheets of porous carbon excellent in electroconductivity are available by this process, there is a demerit that the porosity is larger, the lower the mechanical strength.
The other demerit in the processes is the difficulty of controlling the distribution of pore radii of porous carbon material of shaped articles, which results, for instance, in the frequent occurrence of irregular diffusion of gas on the surface of an electrode made of the shaped article of porous carbon for a fuel cell leading to the reduction of efficiency of generation of electric power.
The object of the present invention is to provide shaped articles of porous carbon not showing the demerits, which are large in porosity, sharp in pore size-distribution and excellent in electroconductivity and mechanical strength. Another object of the present invention is to provide a process for producing the shaped articles of porous carbon.